The present invention relates to an arrangement for the determination of the injection progress in an internal combustion engine or the like having an injection pump and at least one injection valve connected by way of a line with the pressure side of the injection pump, whose injection nozzle is adapted to be closed off by means of a closure element--as a rule in the shape of a needle--which is displaceably arranged in the manner of a piston in a nozzle pre-chamber connected with the line and is acted upon in the opening direction by the pressure of the injection medium supplied by way of the line against a return force, and which additionally includes a stroke transmitter or lift pick-up which is drivingly coupled with the closure element and which is connected with a computer for processing signals that reproduce the stroke or lift position of the closure element.
A corresponding arrangement is disclosed in the DE-OS No. 31 22 553. In this arrangement, the signals of the stroke transmitter or lift pick-up serve to determine the opening degree of the injection valve so that after a determination of the respective pressure conditions at the nozzle, the injection development can be determined. A strain gauge or the like serves for determining the pressure at the injection nozzle, which is arranged at the nozzle body near a feed line for the injection medium extending through the nozzle body and is intended to react to deformations of the nozzle body which are caused by the pressure of the fuel supplied to the nozzle. One starts thereby with the premise that the deformations of the nozzle body take place analogously to the changes of the pressure of the supplied injection medium.
However, with this known arrangement it remains without consideration that deformations of the nozzle body may have very different causes and by no means are determined alone by the pressure of the supplied injection medium. For example, the nozzle body also suffers changes in shape by reason of temperature influences as well as vibrations of an engine. As to the rest, a more or less large phase displacement occurs between pressure changes in the injection medium and the shape changes of the nozzle body. All of these effects lead to the fact that especially with fast-running engines, larger errors have to be accepted if the pressure conditions are determined in analogy to shape changes of the nozzle body.
It is additionally aggravating that the line leading from the injection pump to the injection valve is relieved between injection operations with customary engines under formation of gas and vapor bubbles inside of the line in order to assure a completely satisfactory closing of the injection valve. At the beginning of each injection operation, these gas, respectively, vapor bubbles must be initially filled out by supply of injection medium. This filling operation causes additional pressure fluctuations in the injection medium which again have as a consequence phase-displaced shape changes of the nozzle body. Under some circumstances, also shock waves occur thereby in the injection medium which have a strongly deviating characteristic compared to the vibrations excited in the nozzle holder.
It must additionally be taken into consideration that the opening periods, as well as the closing periods of the closure element fill out in fast-running engines a relatively large proportion with respect to time of the respective injection operation. Errors which occur in the determination of the pressure condition during the opening periods have correspondingly a considerable influence.
An arrangement for the determination of the injection course is disclosed in the publication "MTZ (Motortechnische Zeitschrift) 21 (1960) 5, pages 175 et seq., in which in lieu of the pressure at the nozzle, the pressure at the inlet of the nozzle holder is measured. This arrangement is necessarily inaccurate because during the injection operation necessarily occurring pressure waves in the injection system have a finite expansion velocity so that between the arrival of a pressure wave at the nozzle and at the inlet of the nozzle holder, a larger phase displacement must occur. Especially with high speed engines, this phase displacement cannot be simply neglected. Added thereto is the fact that at the begining of the injection operation, the pressure at the nozzle also rises time-delayed with respect to the pressure at the inlet of the nozzle holder because at first vapor, respectively, gas bubbles must be filled out inside of the line path between the nozzle and the inlet of the nozzle holder. Thus, larger inaccuracies must again be accepted in the determination of the injection development, especially during the opening phase of the closure element of the injection valve.
In a further arrangement known from the publication, MTZ 30, (1969) 7, pages 238, et seq., the fact is utilized that the overall pressure during nonstationary operations is composed at some place of the injection system under consideration, for example, at the location of a pressure transducer arranged remote from the injection nozzle at a feed line of the injection medium, of a rest or quiescent pressure, of a pressure wave preceding to the injection nozzle as well as of a pressure wave returninng from the injection nozzle. As the pressure waves propagate with sound velocity, the phase displacement between the arrival of the preceding or leading pressure wave at the location of the pressure transducer and the arrival of this preceding pressure wave at the nozzle is determined practically exclusively by the length of the path between the location of the pressure transducer and the nozzle. The preceding pressure wave is reflected at the nozzle so that a returning pressure wave propagating again with sound velocity occurs whose running period from the nozzle to the location of the pressure transducer is again determined practically exclusively by the length of the corresponding path. Accordinng to the mentioned publication, the overall pressure measured by the pressure transducer is decomposed by calculation into preceding and returninng waves in order to calculate the respective overall pressure at the nozzle. Pressure sensors directly at the nozzle can be dispensed with therewith, instead the pressure at the nozzle can be determined from a greater distance.
Theoretically this known arrangement distinguishes itself by high accuracy. However, during the filling-out of gas and vapor bubbles, additional pressure waves occur in the injection medium. Additionally, the pressure waves already present in the injection medium are reflected at the gas, respectively, vapor bubbles. These effects have as a consequence that during the opening phase of the closure element of the injection valve considerable errors occur in the determination of the pressure condition at the injection nozzle, if the feed line for the injection medium has been relieved beforehand under formation of gas and vapor bubbles.
Though the injection development is a significant parameter for an optimum combustion progress in an engine, no suitable arrangements are known up to the present which permit an extraordinarily exact measurement, and more particularly also if, at the beginning of the injection operation, gas, respectively, vapor bubbles which had been produced prior thereto in the lines of the injection medium, must be filled with injection medium.
It is therefore the object of the present invention to provide an arrangement which permits to determine the injection course with high accuracy, notwithstanding the aforementioed difficulties also during the opening phase of the closure element of the injection valve.
The underlying problems are solved according to the present invention in that in an arrangement of the aforementioned type, the computer during the time interval of the stroke or lift movement of the closure element between the closing and opening position thereof determines by means of the signals of the stroke transmitter or lift pick-up or by means of the signals of a movement pick-up or transmitter reproducing the velocity of the closure element, determines the velocity and acceleration of the closure element and therefrom the pressure in the nozzle antechamber as well as the volumetric flow leaving the nozzle, respectively, the discharged quantity according to EQU p.sub.D .multidot.A=m.multidot.d.sup.2 h/dt.sup.2 +R.multidot.dh/dt+K.multidot.h+F.sub.1 +F.sub.2 (I) ##EQU1## EQU Q=.intg.dQ/dt (III)
whereby
p.sub.D =pressure in the nozzle antechamber, PA1 p.sub.G =pressure in the combustion space, respectively, on the outlet side of the nozzle, PA1 A=cross section of the closure element acted upon by the pressure p.sub.D in the opening direction, PA1 m=mass of the closure element, PA1 h=stroke of the closure element, PA1 t=time, PA1 R=damping, respectively, friction coefficient of the stroke movement of the closure element, PA1 K=spring constant of the return force, PA1 F.sub.1 =prestress of the return force, PA1 F.sub.2 =friction force, PA1 Q=quantity of the injection medium discharged from the nozzle, PA1 .rho.=density of the injection medium, PA1 f(h,X)=a predetermined function, dependent from the stroke (h) of the closure element and from the pressure factor X, and PA1 X=(p.sub.D -p.sub.G)/p.sub.G =dimensionless pressure factor. PA1 A.sub.e (X)=effective through-flow cross section of the nozzle, depending on pressure condition, and PA1 A.sub.e (X.fwdarw..infin.)=effective through-flow cross section at large pressure factors, for example, X.gtoreq.100.
The present invention is predicated on the general concept to indicate the movement of the closure element between its closing and opening position and to determine therefrom the pressure in the nozzle antechamber, respectively, the flow of the injection medium passing through the nozzle or the discharge quantity thereof. This is possible because the respective path h traversed by the closure element, the velocity dh/dt of the closure element as well as the acceleration thereof d.sup.2 h/dt.sup.2 can be determined, for according to equation I the hydraulic forces exerted by the injection medium on the closure element in the opening direction which are indicated on the left side of the equation I, correspond to the sum of the inertia force opposed by the closure element to a movement, of the friction, respectively, damping resistance opposing a movement of the closure element, of the return force and of the opening force, during the interaction of which the closure element disposed in the closing position commences to open. The particular advantage of the present invention resides in that gas, respectively, vapor bubbles present in the line between the injection valve and injection pump cannot lead to any errors in the determination of the injection course or development, for the stroke movement of the closure element commences only after a practically complete filling of the mentioned bubbles with injection medium.
The values for the cross section of the closure element acted upon by the pressure in the nozzle antechamber in the opening direction, for the mass of the closure element, for the damping, respectively, friction coefficients of the stroke movement of the closure element, for the spring constant of the return force, respectively, of the spring of the injection valve as well as for the prestress of the return force and the friction in the valve which are predetermined nonvariable by the construction of the injection valve, can be fixedly inputted to the computer, for example, by input of corresponding memory values. The same applies for the effective cross section of the nozzle, respectively, the function f(h,X) correlated thereto in equation II.
The pressure in the combustion space, respectively, on the outlet side of the nozzle which counteracts the pressure in the nozzle antechamber is generally of importance only during the needle closure phase. It can be determined by performance graph-interpolation or by an approximation, especially if, for example, with a reciprocating piston engine, the closing phase of the injection valve takes place during a time interval in which the respective piston of the engine assumes a position near its upper dead-center point.
However, the computer may possibly also take into consideration a variation of the combustion space pressure, respectively, of the pressure on the outlet side of the nozzle as a function of crankshaft angle or the like of the engine if the input side of the computer is connected with a corresponding measuring sensor.
Additionally, the volumetric flow can be determined also in approximation by means of the following equations. ##EQU2## where X.sub.GR =limit pressure condition for which in the narrowest flow cross section the static pressure just reaches the value zero (depending on nozzle X.sub.GR =4.+-.2),
In these equations, it is taken into consideration that for all conditions with X.gtoreq.X.sub.GR --and this is the considerably larger proportion--the determination of nozzle counterpressure can be dispensed with because the pressure in the narrowest flow cross section of the injection nozzle has the value 0 [bar].
As soon as the closure element has reached its opened end position, the pressure in the nozzle antechamber, respectively, the flow passing through the nozzle or the discharged quantity of the injection medium can no longer be determined sufficiently accurately alone from the signals of the stroke transmitter or lift pick-up.
In principle, a determination of the flow passing through the nozzles or of the discharged quantity of the injection medium would also be possible in the opened end portion of the closure element if a stroke limitation determining the end position, an abutment arrangement or the like, possessed a sufficiently defined damping as well as a defined spring rate. The injection course could then be determined in all positions of the closure element exclusively from the signals of the stroke transmitter, respectively, of the movement transmitter. However, in practice, this is only possible with difficulty because the constructive expenditures, especially for the stroke limitation or the like, would be very large.
In one embodiment of the present invention, provision is now made to arrange a pressure transducer at the line between the injection pump and the injection valve whose output signals reproducing the line pressure are adapted to be fed to the input side of the computer whereby the computer with fully opened injection valve determines the pressure in the nozzle antechamber, respectively, the flow leaving the nozzle according to a predeterminable functional relationship between pressure in the nozzle antechamber and the line pressure determined by the pressure transducer.
In case the pressure transducer is arranged sufficiently close to the injection valve, the pressure in the nozzle antechamber and the line pressure at the pressure transducer can be set to be approximately equal. Possibly it is also feasible to continuously compare the pressure in the nozzle antechamber determined from the signals of the stroke transmitter with the values for the line pressure determined from the signals of the pressure transducer during the opening movement of the closure element and to determine a correction factor, with which the value of the line pressure must be multiplied in order to obtain an approximate value for the pressure in the nozzle antechamber.
In lieu thereof, it is also possible and preferably so provided with a view to as high an accuracy as possible of the arrangement, to determine the pressure in the nozzle antechamber taking into consideration the pressure waves which occur in the line, respectively, in the nozzle antechamber. For the following is valid for the pressure p.sub.X at the pressure transducer. EQU p.sub.X =p.sub.XV +p.sub.XR =p.sub.0 (IV)
whereby p.sub.O is the stationary pressure in this system, p.sub.XV the pressure of a pressure wave preceding in the direction of the injection valve and p.sub.XR the pressure of a pressure wave returning from the injection valve at the location of the pressure transducer. A corresponding equation is also valid for the pressure p.sub.D in the nozzle antechamber EQU p.sub.D =p.sub.DV =p.sub.DR +p.sub.0 (V)
whereby p.sub.DV is the pressure of the pressure wave preceding to the nozzle and p.sub.Dr the pressure of the pressure wave returning from the nozzle. Furthermore, the following is valid EQU p.sub.DV (t)=p.sub.XV (t=x/a) (VI) EQU p.sub.XR (t)=p.sub.DR (t=x/a) (VII)
whereby t is the time, x is the length of the line between the injection valve and the pressure transducer and a is the sound velocity in the injection medium.
The pressure in the nozzle antechamber can be calculated with increased accuracy on the basis of these relationships taking into consideration the line pressure determined by the pressure transducer, as will be explained more fully hereinafter.
The phases of the injection operation with moving closure element, respectively, with standing-still closure element--especially in the open position--can be determined in a simple manner in that the computer calculates higher derivatives of the progress with respect to time of the needle stroke and examines whether several of these derivatives assume extreme, respectively, zero values either simultaneously, respectively, in a time interval of predetermined short duration. More particularly, if the closure element upon termination of its opening stroke reaches its open end position, the stroke velocity of the closure element is necessarily changed nearly impact-like, whereby the mentioned higher derivatives assume extreme, respectively, zero values. The computer can therewith interpret the point in time of the simultaneous occurrence of extreme, respectively, zero values as the point in time for the fact that the closure element has reached its opened end position.
The same also applies upon reaching the closed end position, for also in that case the stroke velocity of the closure element is changed abruptly.
According to a further particularly preferred embodiment of the present invention, provision is made to measure in the opened end position of the closure element, the force F.sub.A with which the closure element is stressed in the direction of its open position; the computer can determine therewith the pressure p.sub.D in the nozzle antechamber according to the following equation: EQU p.sub.D A=m.multidot.d.sup.2 h/dt.sup.2 +R.multidot.dh/dt+K.multidot.h+F.sub.1 +F.sub.2 +F.sub.A (Ia)
As long as the closure element moves in the opening, respectively, closing direction, F.sub.A =0 is valid, for during these operatign phases, the force-measuring device is not acted upon by the closure element. Accordingly, the equation Ia is identical with the equation I during the opening, respectively, closing phase of the closure element. As soon as the closure element has reached its completely opened position, the two first terms on the right side of the equation Ia disappear if the closure element remains stationary in the completely open condition of the injection valve. During this phase, only the abutment force F.sub.A as well as the other terms predetermined by the construction of the injection valve need to be taken into consideration insofar as the closure element does not carry out any post-hunting or after-oscillations.